1. Field of the Invention
This invention is related to a method and apparatus for producing a pattern corresponding to a fingerprint and more particularly to a method and apparatus for scanning a finger with a monochromatic light beam and for producing an output which corresponds to the ridges and troughs in the finger.
2. Description of the Prior Art
The use of fingerprints for determining the identity of an individual is a well-established technique of identification. Several prior art methods exist for producing an image which corresponds to the fingerprint. The most basic technique is the application of ink to the finger and then rolling the finger on a piece of paper. This produces an inked image which corresponds to the fingerprints. This technique has had several disadvantages. The four most obvious disadvantages are the fact the process is very messy because of the use of the ink and very slow because of the necessity of inking each finger and then rolling each finger onto the paper, lack of uniform quality between prints, and the rubber stamp effect distorting prints.
Another technique which has been used is to flood the surface of the finger with light which is then reflected by the surface. Due to the different reflective characteristics of the ridges and troughs, an image is produced which corresponds to the fingerprint. The reflected light may be passed through a transparency of a previously recorded fingerprint to produce an output which is indicative of the comparison of the fingerprint to the previously recorded fingerprint. This technique is disclosed in U.S. Pat. No. 3,511,571. The reflected light may also be scanned to produce an output indicative of the fingerprint. This technique is disclosed in U.S. Pat. No. 3,200,701. Systems using the technique of flooding the surface of the finger with light from a source do not have sufficient resolution to provide the required accuracy in many cases. This is due to the fact that the difference in reflected light from the ridges and troughs is relatively small. Furthermore, the signal derived from the reflected light is not amenable to automated data processing.